Carboranyl burning rate accelerators, also referred to as carborane catalysts, have been of interest in the preparation of ultrahigh-burning-rate propellants of the composite-modified, double-base, composite (the latter having terminal functionality of carboxyl and hydroxyl), or difluoroamino-plasticized, ethyl acrylate-acrylic acid-based types.
The presently-used procedure for the synthesis of currently useful carborane catalyst include:
(1) Preparation of diborane;
(2) Thermolytic conversion of diborane into decaborane; and,
(3) Reaction of decaborane with a substituted alkyne to yield the carboranyl burning-rate accelerator.
The severe limitations of the presently-used method are low conversions, low yields, and the resulting extremely high costs of the carboranyl chemicals. In view of the high costs and other relevant limitations, the need for a better synthesis method is much desired.
A particular route for the synthesis of diborane via the reduction method of boric oxide (or boric acid or metal borate) in the presence of aluminum powder, anhydrous aluminum chloride, and sodium chloride has been considered for the source of diborane for conversion to decaborane which is then reacted with a selected alkynyl alkanate or alkyne to form a variety of carboranyl burning rate catalysts. Since this route for the synthesis of diborane requires high temperature and high pressure operation it imposes disadvantages and limitations which encourage the development of a less involved process for producing a precursor decaborane derivative compound which can subsequently be converted to the carboranyl burning rate catalysts.
Therefore, an object of this invention is to provide a better synthesis method for producing precursor decaborane derivatives which can be readily converted to a precursor compound for carboranyl burning rate catalysts which have a proven performance record.
A further object of this invention is to provide a synthesis method for producing a precursor compound for preparing a variety of carboranyl catalysts by the selection and addition of a second reactant to yield the final desired carboranyl catalyst.
Still, a further object of this invention is to provide a method of synthesis for producing a precursor compound which does not require the production of diborane and decaborane intermediates that are highly toxic and spontaneously inflammable in air at high concentrations.